(1) FIELD OF THE INVENTION
This invention relates to vibration generating apparatus suitable for use with vibration type pipe laying systems, vibration type pile impacting systems, vibration type compacting machines, etc., and more particularly it is concerned with a vibration generating apparatus which generates, while producing a thrust (a force acting in the direction of a center axis of vibration type pipe laying system, a vibration type pile impacting system or a vibration type compacting machine), a vibratory force directed substantially perpendicular to the thrust.
(2) DESCRIPTION OF THE PRIOR ART
One example of the vibration generating apparatus of the prior art is disclosed in Japanese Patent Application Laid-Open No. 123392/82 as being suitable for use with a vibration type pipe laying system.
This type of vibration generating apparatus of the prior art comprises a support and vibrating body generally formed in a cylindrical configuration and provided with a forward end portion of a conical shape, a rotary shaft coaxially rotatably mounted within the support and vibrating body and having an eccentric weight mounted thereon, and a drive motor connected to the rotary shaft. Actuation of the drive motor causes the rotary shaft to rotate about its center axis and causes the support and vibrating body to vibrate in a direction substantially perpendicular to the center axis of the rotary shaft by virtue of the eccentric weight supported on the rotary shaft.
The vibration generating apparatus of the aforesaid construction is connected at a rearward end of the support and vibrating body to a forward end of a foremost one of a plurality of pipes to be laid underground, with a rearward end of a rearmost one of the plurality of pipes to be laid being connected to a presser device located in a starting pit. Thus, the vibration generating apparatus is set into a vibration type pipe laying system. The vibratory force generated by the vibration generating apparatus would reduce firmness of the ground and allow the pipes to be laid to be pressed forwardly by the presser device toward a destination pit. The vibration type pipe laying system incorporating therein the vibration generating apparatus of the aforesaid construction offers the advantage that it is higher in operation efficiency than a press-in type pipe laying system wherein pipes to be laid are directly pressed by a presser device and propelled. Additionally, the presser device used with the vibration type pipe laying system can be smaller in size than that used with the press-in type pipe laying system. By supplying a viscosity imparting liquid through the leading end of the support and vibrating body, soil particles produced as the ground is loosened and crushed by the vibration generating apparatus are mixed with the viscosity imparting liquid to form a slurry which fills the gap between the vibration generating apparatus and the pipes to be laid and the ground, so that the frictional resisting force exerted by the ground to the apparatus and the pipes is further reduced. This is conducive to improved operation efficiency and permits a compact size to be obtained in a presser device.
Some disadvantages are associated with the vibration generating apparatus of the aforesaid construction of the prior art. In this apparatus, the support and vibrating body vibrates as a whole. Thus, when pipes to be laid are connected to the support and vibrating body, the vibration generating apparatus is connected to the pipes to be laid in rigid coupling, so that the vibration of the apparatus would be directly transmitted to the pipes to be laid. This cause a portion of the vibration generated by the apparatus to extend to the pipes to be laid, and therefore the concurrent vibration of these members makes it necessary to increase the size of the vibration generating apparatus to obtain a necessary vibratory force of a high magnitude at the support and vibratory body.
The vibration generating apparatus under discussion would suffer the aforesaid disadvantage also when it is incorporated in a vibration type pile impacting system or a vibration type compacting machine, because the vibration of the apparatus would be transmitted to other parts of the vibration type pile impacting system or vibration type compacting machine.
To obviate the aforesaid disadvantage, a vibration generating apparatus has been developed which is capable of preventing the vibration from being transmitted to the pipes to be laid and other parts of the pipe laying system.
Japanese Patent Application Laid-Open No. 146896/82 discloses this type of vibration generating apparatus as incorporated in a vibration type pipe laying system. This vibration generating apparatus comprises a support body formed in a generally cylindrical configuration, a vibrating body having a forward end portion of a conical shape and a substantially cylindrical portion coaxially inserted in the cylindrical support body, a plurality of vibration absorbing rods of a small diameter for connecting a rearward end of the vibrating body to a forward end of the support body, the rods having opposite ends fixed to the rearward end of the vibrating body and the forward end of the support body in such a manner that the plurality of rods are arranged in a circle concentric with the support body and cylindrical portion of the vibrating body, and a bellows-like member of a resilient material interposed between the forward end of the support body and a rear surface of the conical forward end portion. A rotary shaft is coaxially rotatably mounted in the cylindrical portion of the vibrating body and mounts thereon an eccentric weight, and a drive motor is connected to the rotary shaft. A vibration type pipe laying system provided with this vibration generating apparatus offers the same advantages as the vibration type pipe laying system provided with the vibration generating apparatus of the prior art described previously.
An additional advantage offered by the last mentioned vibration generating apparatus is that the provision of the rods of a small diameter between the support body and vibrating body enables vibration of the vibrating body (vibration directed perpendicular to the axis of the support body and the cylindrical portion of the vibrating body) to be absorbed by deflection of the rods of the small diameter from the axis of the support body and the cylindrical portion of the vibrating body, while a thrust is applied by the presser device to the vibrating body, so that the vibration of the vibrating body is not transmitted to the pipes to be laid through the support body. Stated differentily, the vibrating body is connected to the pipes to be laid in flexible coupling through the support body and rods of the small diameter. Thus, the disadvantage of the first mentioned vibration generating apparatus that it should be large in size to produce a vibratory force of a high magnitude because its vibration is transmitted to pipes to be laid when it is incorporated in a vibration type pipe laying system and to other parts when it is incorporated in a vibration type pile impacting system or a vibration type compacting machine is eliminated.
However, in the last mentioned vibration generating apparatus wherein the rods of a small diameter are provided to serve as vibration absorber means, another problem has been raised. That is, since the rods of a small diameter interposed between the support body and vibrating body must bear a thrust applied by the presser device, the rods might be ruptured when the thrust applied thereto is high in magnitude.